Extended range RF-ID transponder

Abstract: An transponder arrangement (10) for use with tyres (20) is described. The arrangement (10) includes an antenna (14) which is mounted about the tyre's(20) perimeter. The antenna (14) preferably has a coupling coil (16) at one end. A transponder (12) is preferably located close to the coupling coil (16) and is preferably loosely coupled to the coupling coil (16). The RF-ID efficiency of the arrangement (10) is generally optimized for this type of application by the long but narrow antenna solution and by the simple fact that coupling an antenna (14) to a transponder (12) amplifies the emission of the transponder's signal relative to the noise, thus improving the signal-to-noise ratio of the RF-ID system. The degree of coupling between the antenna (14) and the transponder (12) is not particularly critical. The antenna (14) acts to extend the reading range for the interrogator (24) to be generally, radially symmetric about the tyre (20). Other arrangements are disclosed.

Description: Field of the Invention This invention generally relates to the extension of a planar and/or vertical reading range in existing interrogator/transponder RF-ID systems and modification of the shape of the inherent transponder or reader antenna pattern to better meet specific applications. This invention relates more specifically to a tyre RF-ID system as defined in the precharacterizing portion of claim 1. Background of the Invention Applications of RF-ID systems have been used within the tyre industry to identify and monitor tyres within warehouses or in actual operation mounted to vehicles. Ideally, because the angular position of the tyre is not known, the reading range by an interrogator would be symmetric about the circumference of the tyre. Prior art systems might forego this ideal characteristic symmetry, thereby causing difficulties in obtaining consistent communications between the interrogator and the transponders. Other prior art systems such as described in the PCT patent application 90/12474 have used a loop antenna, but have required an electrical contact between an IC or other control circuitry and an antenna ,which is routed about the tyre's circumference. This use presents difficulties in maintaining a hermetic seal about the electronic circuitry. Such a system is further more difficult to manufacture and is less mechanically reliable. Furthermore, the reading range is reduced in prior art systems having a loop antenna because the loop connected to the transponder yields a lossy, lower Q-factor antenna. From EP-A-0 505 905 an integrated circuit transponder in a pneumatic tyre for use in tyre identification is known. The transponder has a coil antenna of small enclosed area as compared to the area enclosed by an annular tensile member comprising a bead of the tyre. The annular tensile member, during transponder interrogation, acts as the primary winding of a transformer. The coil antenna is loosely coupled to the primary winding and is the secondary winding of the transformer. The coil antenna is substantially planar in shape, and, when positioned between the innerliner of the tyre and its carcass ply, the transponder may include a pressure sensor responsive to tyre inflation pressure. Summary of the Invention According to one aspect of the present invention, there is provided a tyre RF-ID system to be identified by an interrogator unit operable to send a wireless RF interrogator signal, said system comprising: the features defined in claim 1. The magnetic coupling eliminates the need for a galvanic contact between the transponder and the antenna. Further, the transponder can be easily hermetically sealed. The coupling of the antenna coupling coil to the transponder coupling coil is preferably loose for a tuned-type transponder to maintain the high "Q" and to avoid detuning and damping. Both effects of lowering the "Q" and detuning or damping the transponder may adversely affect the receiving function of the transponder and the reading range of the transponder. The RF-ID efficiency of the arrangement is generally optimized for this type of application by the long but narrow antenna solution and by the simple fact that coupling an antenna to a transponder, amplifies the emission of the transponder's signal relative to the noise, thus improving the signal-to-noise ratio of the RF-ID system The transponder is mounted by an adhesive patch or other means in proximity to the coupling coil. The coupling distance between the antenna and the transponder is not particularly critical The antenna acts to extend the reading range for the interrogator to be a long range which is generally, radially symmetrical about the tyre. According to further embodiments of the invention, the interrogator and the transponder may be in full duplex or in half duplex communication. Brief Description of the Drawings Reference will now be made, by way of example, to the accompanying drawings in which: Fig. 1 shows the transponder/antenna configuration according to the invention; Fig. 2 shows a transponder within a coupling distance of the coupling coil of the antenna; Fig. 3 shows the preferred embodiment transponder loosely coupled to the antenna within a tyre; Figs. 4a-b show exemplary cross sections for View A referenced in Fig. 3 ; and Fig. 5 shows a graph illustrating the uncritical relation of the reading range to the coupling distance, d couple . Detailed Description of the Preferred Embodiments Fig. 1 shows a first preferred embodiment of the extended range transponder/antenna arrangement 10 . The transponder 12 is loosely coupled to the coil 16 , which forms one end of the long and narrow antenna 14 . The coil 16 consists of, for example, 3-4 windings. Although one example of providing loose coupling between the coupling coil 16 and the transponder 12 has been described, there are several methods in which to provide the loose coupling to the transponder as will be appreciated by one of ordinary skill in the art. For example, the coil 16 might be a printed flat coil. As other alternatives: a single winding coil 16 could be used; Indeed any number of windings from one to many could be used to advantage. Fig. 2 shows a transponder 12 within a coupling distance d couple of the coupling coil 16 of the antenna 14 . The effect of the coupling distance, d couple and use of different materials for the antenna 14 is shown in Fig. 5 . As can be seen in Fig. 5 , the coupling distance d couple is not critical and is typically between 1 and 10 mm. The effective reading range is somewhat dependent on the width of the antenna, W. The width, W, is preferably at least 1 cm. Also shown in Fig. 5 is the relative reading range for using steel (the "A" graph) or copper (the "B" graph) as the antenna 14 . Other materials might be used to advantage by one of ordinary skill in the art. The skilled artisan would select a material based on well-known properties such as conductivity, strength coefficients of expansion, and compatibility with the tyre material. It is therefore intended that the appended claims encompass any such modifications or embodiments. Fig. 3 shows the preferred embodiment transponder 12 loosely coupled to the antenna 14 within a tyre 20 . As mentioned, the antenna 14 extends the effective reading range between the interrogator 24 and the transponder 12 . The dashed lines of Figure 3 illustrate the bounds of a typical reading range for the preferred embodiment system. The measurements given relating to the dashed lines are with respect to the perimeter of the tyre 20 . Measurement d 1 is the distance from the perimeter of the tyre at the angular position of zero degrees with respect to the transponder (i.e., the position closest to the transponder 12 ). A typical measurement for d 1 is approximately 20 cm. Typical measurements for d 2 , d 3 , and d 4 which are located at 90, 180, and 270 degrees, respectively, in relation to the angular position of the transponder 12 . Figs. 4a-b show exemplary cross sections of View A from Fig. 3. Fig. 4a shows the exemplary cross section for the mounting of antenna 14 on the sidewall 30 of a tyre 20 . The attachment method for this particular embodiment might be to affix the antenna 14 and the transponder 12 using a patch 32 . Fig. 4b shows the exemplary cross section for the mounting of antenna 14 within the sidewall of the tyre 20 in an integrated manufacturing process in which the antenna and transponder might be formed directly within the structure of the sidewall 30 of the tyre 20 . According to a preferred embodiment of the invention, the transponder/antenna configuration is easily applied to a more detailed example of an RF-ID system. For example, this RF-ID system has a transponder 12 with an identification code, which when attached to an object, identifies and discriminates one object from another. The coupling coil 16 is loosely coupled to the transponder 12 , and the transponder/antenna configuration of Figure 1 is attached to a tyre 20 . When a read is wanted to locate a particular tyre 20 , the hand-held interrogator 24 is held within the extended range of the transponder 12 , and an interrogation pulse is transmitted. The transponder 12 receives, rectifies and stores the interrogation pulse energy, and transmits an identification code in response to an adequate amount of interrogation energy received. The hand-held interrogator 24 receives the identification code from the transponder 12 and processes the identification code as desired. One advantage of having the transponder/antenna arrangement 10 versus having just the transponder 12 attached to the tyre 20 , is the greater flexibility in locating the hand-held interrogator 24 when performing a read of the transponder identification code. Due to the transponder/antenna arrangement 10 , the hand-held interrogator can identify the tyre 20 anywhere along the perimeter of tyre 20 , instead of in the relatively immediate area of the transponder. According to a another preferred embodiment of the invention, the transponder/antenna configuration is applied to an RF-ID system in which sensory information is read from the transponder 12 . In this embodiment, the transponder is typically activated during a powering phase. During this phase a continuous wave signal would be sent from the an interrogator 24 to the transponder 12 . After a predetermined period of time, the interrogator ceases the continuous wave power signal and may then transmit command data to the transponder 12 . Because the extended range antenna described in this application is equally effective for coupling interrogation signals into the transponder as for transmitting response signals from the transponder, the range over which the commands can be sent to the transponder 12 is increased. Further, the range over which the transponder can be powered is also increased. Once the transponder 12 has been commanded by the interrogator 24 to perform an action such as read a sensor or another action, the transponder 12 is then operable to enable the sensor (if necessary) and to digitize the data read from the sensor. For example, this sensor might return a pressure or temperature reading from within the tyre. In this exemplary procedure for working with sensory RF-ID systems, the transponder then stores this information in a shift register. Upon completion of the digitizing and storage of the sensory information, the transponder 12 then can return this information by modulating a carrier with the data stored in the shift register. This data might include relative sensory information with calibration information such that the interrogator 24 can calculate the absolute sensory information, or the transponder 12 night calculate the absolute sensory information and pass this information directly on to interrogator 24 . An example of how the reading and writing procedures might be implemented is provided in coassigned U.S. Patent No. 5,450,088. A few preferred embodiments have been described in detail hereinabove. It is to be understood that the scope of the invention also comprehends embodiments different from those described, yet within the scope of the claims.

Claims: A tyre RF-ID system to be identified by an interrogator unit (24) operable to send a wireless RF interrogator signal, said system comprising: a tyre (20); a transponder (12) located on said tyre (20), said transponder (12) having a transponder coupling coil, said transponder (12) being operable to receive said interrogation signal and generate a transponder response signal; and an antenna (14) located approximately circumferencially on said tyre (20) for receiving said interrogation signal and for transmitting said transponder response signal; characterized in that said antenna (14) has two ends; and that said system further comprises an antenna coupling coil (16) electrically connected to said two antenna ends and located in close proximity to said transponder coupling coil and magnetically coupled thereto, said coupling coils being for magnetically coupling said interrogation signal from said antenna (14) to said transponder (12) and for magnetically coupling said transponder response signal from said transponder (12) to said antenna (14). The tyre RF-ID system of claim 1, wherein said interrogator (24) and said transponder (12) are in full duplex communication. The tyre RF-ID system of claim 1, wherein said interrogator (24) and said transponder (12) are in half duplex communication. The tyre RF-ID system according to claim 2 or claim 3, wherein said transponder coupling coil is loosely coupled to said antenna coupling coil (16). The tyre RF-ID system according to any preceding claim, wherein the radiation pattern of said antenna (14) lies circumferencially about said tyre (20). The tyre RF-ID system according to any preceding claim, wherein said transponder (12) is attached to the tyre (20) with an adhesive patch. The tyre RF-ID system according to claim 6, wherein said transponder coupling coil is located within 10 mm of said antenna coupling coil (16). The tyre RF-ID system according to any preceding claim, wherein said antenna (14) is copper. The tyre RF-ID system according to any of claims 1 to 7, wherein said antenna (14) is steel.

Inventors: SCHUERMANN JOSEF H, SCHUERMANN, JOSEF H.
Applicants: TEXAS INSTRUMENTS DEUTSCHLAND, TEXAS INSTRUMENTS DEUTSCHLAND GMBH
Application year: 1994
Main classification: G06K7
IPC codes: G06K19, H01Q1, H04B5, G06K7